Plotting devices are well known for the preparation of engineering drawings, geophysical representations, apparel patterns and markers (a nested array of patterns) and other pictorial representations on paper stock.
These plotting devices generally use either specific cut sheet paper sizes or operate with continuous paper rolls. In the former application the length of the plotted image is generally rather short, from a few inches to a few feet, and thus the error accumulation as a function of the length of the plot is limited. Another class of plotters using continuous rolls of paper, which is more related to the present invention, can generate plots of considerable length, from a few feet to many yards, and thus the accumulation of error as a function of plot length can become significant. Thus, it is an object of the present invention to provide a compact plotter which can generate long plot lengths without an accumulation of error.
Previously developed plotters capable of operating with continuous paper rolls have generally fallen into the categories of either flat bed (or table type) plotters or upright graphical plotters. The flat bed plotters are computerized for controlling a marking pen in an X-Y plane to reproduce a plotted image on a sheet of paper that is normally laying flat and maintained stationary on a large horizontal plotter table. Each incremental movement of the pen in both the X and Y directions is controlled by the computer and is driven by highly responsive servo systems. Since the plotted image is generated by having the pen actually draw the contour, the mechanism that drives the pen must have high speed and high acceleration capabilities in order for the plotter to have a sufficient throughput. Furthermore, if the length of the plotted image exceeds the length of the plotter table, a precision paper advance must be made in order to produce a clean area of paper upon which the plotted image is continued. Thus, prior flat bed plotters have been of substantial size in the horizontal plane and occupy a considerable amount of floor space. In addition, these plotting devices are expensive due to the complexity of the mechanisms required to drive the pen and to provide a precision paper advance.
Upright graphical plotters which are more closely related to the present invention have been developed wherein a marking head is reciprocated in a rectilinear path while the paper moves transversely thereto. In order to create accurate long length plots these devices have resorted to very sophisticated precision paper advance mechanisms or to special papers such as those types having an array of holes on each side of the paper along its entire length which in turn can mate with a sprocket driven device on the plotter. Thus, in previously developed upright plotters either the equipment has been very expensive due to their precision mechanisms or the paper required has been very expensive due to its special nature.
It may be seen from the foregoing that a need has arisen for a highly accurate upright plotting device that requires little floor space and that can accurately produce very long length plots with low cost, and nonsophisticated mechanisms for controlling paper movement and the motions of the print head.